In an internal combustion engine, there are installed blowby gas paths for guiding blowby gas, passing from a combustion chamber via an intermediary between a piston and a cylinder sleeve and leaking to a crank chamber, returning gas again to the combustion chamber and combusting the blowby gas. The blowby gas path is installed to open at one end to a crank chamber, to pass through a cylinder block and a cylinder head and to open at its other end to a breather chamber of a head cover.
Blowby gas guided by the blowby gas paths to the breather chamber, is separated of oil mist included in the gas, sucked to an intake system via a PCV valve operated by intake negative pressure and is combusted by being supplied to the combustion chamber along with intake air.
Such blowby gas path structures of an internal combustion engine have been disclosed in JP-B-5-3692U, JP-A-63-79417U, JP-A-64-49617U, JP-A-62-64805U, JP-A-58-62113U, JP-A-2-52912U, JP-A-2-94312U and JP-A-3-54224U.
According to the disclosure of JP-B-5-3692U, there is installed a breather path passing from a crank chamber of an engine and having a substantially horizontal axial line to a cylinder and to an upper face side of a cylinder block to communicate with a cam chamber of a cylinder head.
According to the disclosure of JP-A-63-79417U, in an engine in which a cylinder head and a cylinder block are fixed by through bolts penetrating the cylinder block, there are installed communication holes for communicating the crank chamber and the cam chamber via the through bolts.
According to the disclosure of JP-A-64-49617U, an engine installed with a projected portion projecting outside at a side wall of a cylinder head supports a balancer shaft. There is a volume chamber above the projected portion of the cylinder block and there is a blowby gas path for communicating a crank chamber with a valve operating chamber via the volume chamber.
According to the disclosure of JP-A-62-64805U, there are installed oil dropping paths and blowby gas paths extending upward from a crank case at a side face of a cylinder block installed with oil dropping paths and blowby gas paths. The oil dropping paths and the blowby gas paths of the cylinder block communicate at positions of a cylinder head outside of attaching bolts.
According to the disclosure of JP-A-58-62113U, a midway of a blowby gas path in a cylinder block and a cylinder head is formed substantially in a crank shape.
According to the disclosure of JP-A-2-52912U, a breather chamber is connected to a lower side of a breather path communicating with a crank case and a cylinder head and there is installed a bypass path for communicating the breather chamber and an upper side of the breather path.
According to the disclosure of JP-A-2-94312U, a breather apparatus includes a breather chamber lid which is attached to an opening portion of a breather chamber at a side face of a crank case and a breather pipe for connecting the breather chamber and an air cleaner which is attached to the breather chamber lid. In an attitude of rolling an engine where the breather chamber is disposed on the lower side, an opening portion of the breather chamber lid opens to the breather chamber, and projects in a pipe-like shape on an upper side of a blowby gas guide out port of the breather chamber.
According to the disclosure of JP-A-3-54224U, there is installed a ventilation path constituting a portion of a blowby gas recirculating path that introduces new air into a blowby gas exhaust path. The ventilation path is arranged to pass through a head cover, a cylinder head and a cylinder block successively from the upstream side. A downstream side end portion thereof is opened to a crank case. In the meantime, a path sectional area of the ventilation path at an intermediary from a position at a vicinity of a matching face of the cylinder head and the cylinder block to an opening portion of the crank case, is set to be larger than a path sectional area of the ventilation path in the cylinder block on a side upstream therefrom and larger than a sectional area of the ventilation path in the cylinder head.
In the meantime, there is an internal combustion engine having a plurality of cylinders aligned in series. According to the blowby gas path structure of such an internal combustion engine, there is one in which a plurality of blowby gas paths are installed and disposed on one side of the internal combustion engine in a width direction among cylinders, and aligned independently from each other.
However, when path sectional areas of the plurality of blowby gas paths differ from each other, a blowby gas flow rate of a blowby gas path having a larger path sectional area becomes larger than that of a blowby gas path having a smaller path sectional area and causes a drawback in that much oil mist is conveyed into a breather chamber by the blowby gas path having the larger path sectional area and the oil separating function is deteriorated.